DETERMINATION OF CARBOHYDRATES IN FRUIT JUICES BY CAPILLARY ELECTROPHORESIS AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A capillary zone electrophoresis (CZE) method with indirect UV detection was adapted for the routine determination of carbohydrates in a variety of fruit juices. The method was optimized with respect to the effect of buffer pH, temperature and capillary length. Potassium sorbate was chosen as the background electrolyte and chromophore for UV detection at 256 nm. Optimum separation conditions were found with a buffer of a pH of 12.2-12.3 and a subambient temperature of 15 degrees C. The optimized CZE method was compared with a routine method for the determination of sugars in fruit juices, a high-performance anion-exchange chromatographic method with pulsed amperometric detection (HPAEC-PAD), with respect to separation efficiency, sensitivity, linearity and repeatability. The CZE method showed a 10-20-fold increase in separation efficiency compared with the HPAEC-PAD method, but the amperometric detection in the latter proved to result in detection limits of 2-3 orders of magnitude lower than those obtained by indirect UV detection. Both methods showed good linearity in the investigated concentration ranges and good repeatability for migration times and peak areas. CZE with commercial instrumentation was applied to the routine determination of carbohydrates in fruit juices such as orange, apple and grape juice. The quantitative CZE results with internal calibration showed no significant differences from those for the HPAEC-PAD reference method. It was demonstrated that capillary electrophoresis (CE) can be applied in a routine food testing laboratory. The method is simple, inexpensive and easy to implement and will further broaden the application range of CE in food analysis.